1. Field of the Invention
The present invention relates to a rotary swash plate type of axial pump provided with plungers which are forced to execute a stroke movement by a rotary swash plate which is rotated together with a drive shaft, and more particularly, to a device for controlling the amount of the stroke of the plunger in such a type of pump.
2. Description of the Related Art
Two types of axial plunger pump, a rotary swash plate type (see, for example, Japanese Unexamined Patent Publication No. 63-61779) and a fixed swash plate type (see, for example, Japanese Unexamined Utility Model Publication No. 58-15665) are known. In the rotary swash plate type axial pump, a cylinder block in which plungers are slidably accommodated is stationary while a swash plate is rotated. Conversely, in a fixed swash plate type, the cylinder block is rotated while the swash plate is stationary. To vary the output of the pump, the angle of the swash plate can be varied for both the rotary swash plate pump and the fixed swash plate type pump.
The most important advantage of the rotary swash plate type pump over the fixed swash plate type pump is that, because the massive cylinder is not rotated, the inertia of the moving part of the pump is reduced, which allows the upper limit of the rotational speed of the pump to be increased and wear of the moving parts to be reduced, thus prolonging the service life of the pump. In the rotary type pump, the mechanism for controlling the output rate controls the angular position of the rotating swash plate, and therefore, some of the parts used for controlling this angular position rotate together with the swash plate, and thus these parts are soon worn. Furthermore, the construction is complicated because these parts must be rotated while executing the functions of controlling the angular position of the swash plate, but the alignment of the parts is easily lost due to the resulting wear, and thus the precision of the control is also easily lost.